In vehicles of today it is common to use an exhaust driven turbocharger for compressing air to an inlet manifold of an engine. The turbocharger revs up dependent on the exhaust flow, which in turn is dependent on engine speed and engine torque. Hence, turbocharger response is a well-known problem with turbocharger engines at low engine speeds. This problem becomes worse with the new technologies to reduce CO2, downspeeding and downsizing with increased boost due to the fact that it needs more energy to build up the higher boost pressure. The response problem is a limiting factor in CO2 reduction especially in real world driving due to that an acceptable drivability of the vehicle needs an amount of power margin to handle instant power demands without need of gear shifting, The instant power demands may be from road inclination, small accelerations, accessories, etc. In order to use as much of the energy from the exhaust gas as possible, it is known to use two turbochargers in series, one high pressure turbocharger that compresses the inlet air before the inlet manifold but also a low pressure turbocharger that compresses air before entering the high pressure turbocharger. The response problem according to the above is known also for a two-step system, but an additional problem is the synchronization of the two turbochargers in order to utilize them in optimal way depending on engine load.
It is known to use various compressors connected to the inlet manifold for response assistance by feeding air to the inlet side before the turbocharger has revved up. The mechanical compressor is complex, expensive, has low durability, NVH (Noise, Vibrations, Harshness) problems, difficult to control and is noisy.
There is thus a need to find a solution that is cost efficient, durable, produces low noise and improved response.